(1) Field of the Invention
This invention relates to sustained release pesticide compositions and processes for making the compositions. More particularly, this invention relates to an improved lignin-based carrier for the controlled release of organic water-insoluble pesticides or water-soluble salts of pesticides.
Technically, advantages to controlled release of pesticides are many and varied. The incorporation of a toxicant into a matrix offers protection to the pesticide from the degrading processes normally taking place. This makes possible the use of compounds less stable than halogenated hydrocarbons (e.g., carbamates, organophosphates, pyrethroids). Secondly, new uses for existing pesticides can be found. For example, Parathion and its derivatives cannot, because of degradation, be used in the soil unless very frequent applications at high dosage levels of material can be tolerated. Shelf life stability of formulations may also be increased for the above-mentioned reasons. In many underdeveloped parts of the world, pesticides are often applied by hand by individuals possessing little or no protective equipment. The slowed release of the toxicant results in a reduced toxicity to the persons working with it. Specialty applications of pest control materials are realized through adoption of controlled release. An example can be found in animal feed throughs where a rapid and pin point release of a biologically active substance is desired.
(2) Prior Art
As presently known, pesticides often have short useful lives; because they are degraded by bacteria to biologically inactive metabolites, or leached by rain into the subsoil where they are inaccessible to the pest they intend to control, or rendered inactive by volatilization, or by ultraviolet catalyzed degradation from exposure to sunlight. It is, therefore, desirable to provide a system whereby proper amounts of a biologically active organic pesticide may be continually released over a relatively long period of time. An up-to-date discussion of controlled release of pesticides and the desirability of using controlled release systems were presented by Allan et al. in an article entitled "Pesticides, Pollution and Polymers" in Chem Tech (March 1973).
Methods of obtaining controlled release or sustained release of pesticides are numerous in the prior art. U.S. Pat. No. 3,516,941 to G. W. Matson, for example, describes a method for obtaining controlled release of droplet size materials through microencapsulation.
U.S. Pat. No. 3,393,990 to R. J. Geary describes a pesticide composition wherein the pesticide is ground to a large surface area to exhibit its greatest effectiveness. The pesticide is held in place with a stabilized interpolymer substrate while it is slowly released.
U.S. Pat. No. 3,172,752 to H. L. Pierce is directed to a composition for the controlled release of an active agricultural substance. The composition is an enlarged particle formed from ground, expanded perlite which is properly sized and dried. The expanded perlite particles are coated and impregnated with hardened, slowly dissolving holding material of a viscous character before hardening. At least one active agricultural substance is uniformly dispersed therethrough and held to the particle covering the surfaces and filling the pores to intimately and tightly bind the agricultural substance to the perlite particles.
Another method for controlling the release of pesticides is provided in U.S. Pat. No. 3,813,236 to G. G. Allan. The Allan patent discloses chemical co-valent bonding of a pesticide to a lignin polymeric substrate. The pesticide is released by destruction of co-valent chemical bonds.
This invention, on the other hand, produces sustained release compositions by physically mixing pesticides with an improved carrier comprising a cross-linked reswellable lignin gel. It is, therefore, the general object of this invention to provide a sustained release composition having a pesticide interspersed and physically bound throughout a cross-linked reswellable alkali lignin gel.
Another object of this invention is to provide processes for interspersing a pesticide throughout an alkali lignin gel via physical contact forming a composite.
It is a specific object of this invention to provide a controlled release pesticide system comprising as a composite, a pesticide interspersed throughout an epichlorohydrin alkali lignin matrix whereby the release rate of the pesticide is accomplished through diffusion of the active ingredient through the alkali lignin matrix or through degradation or dissolution of the lignin matrix or a combination of both.
It is still another object of this invention to provide lignin composites containing pesticides which are stabilized against the degrading effects of sunlight.
It is an even further object of this invention to provide pesticide-containing composites which have controlled release that are substantially uneffected by rain.
It is yet another object of this invention to provide lignin matrixes containing pesticides which resist the action of micro-organisms.
Still another object of this invention is to provide controlled release pesticidal systems which maintain maximum and effective activity over prolonged periods of time under normal plant environmental conditions.
Other objects, features and advantages of this invention will become evident on reading the foregoing detailed description.